[test][AliasAnalysis] Add some baseline tests in preparation for getModRefInfoMask().

This commit adds some tests in preparation for D136659, which allows alias
analysis to treat locally-invariant memory pointed to by readonly noalias
pointers the same as globally-invariant memory in some cases. The existing
behavior for these tests is marked as expected and will be changed when that
diff lands.

Differential Revision: https://reviews.llvm.org/D136993